Height adjustment of back rests

ABSTRACT

The invention concerns the height-adjustment of the back-rests of chairs, especially office chairs, consisting of a housing (1) in which a flat back-rest carrier (2) is held by a ball-stop clamp (3, 4), the back-rest carrier (2) being provided with a series of indentations or holes (3) arranged behind one another in an axial direction for the stop balls (4) which are held in the indentations or holes (3) by means of a spring-loaded clamping bevel (5&#39;). The clamping bevel (5&#39;) can be brought out of contact by a push-button (8) guided sideways from outside the housing against the spring force, spring-loaded means (10, 11) being arranged in the housing (1) for the prevention of sideways play of the back-rest carrier (2).

DESCRIPTION

The invention relates to a height adjustment for back rests.

Such a height adjustment for back rests of chairs, in particular officechairs, consisting of a housing in which a flat back rest carrier isheld by a detent ball clamping arrangement, whereby the back restcarrier is provided in axial direction with successively arrangedindentations or openings for detent balls which are held in theindentations or openings by a spring-loaded clamping bevel, and wherebya push button that extends laterally from the housing can be used tomove the clamping bevel against the elastic force to disengage it, isknown, for example, from EP-A-O 264 555.

The objective of the present invention is to create a height adjustmentof the type mentioned above which is easy and comfortable to operate andwhich functions reliably.

Further developments and advantageous embodiments of the invention aredescribed hereinafter.

According to the invention, spring-loaded means are arranged in thehousing to prevent lateral play of the back rest carrier. Thanks to thismeasure, the back rest cannot tilt and rock. According to a preferredembodiment of the invention, the means to prevent the lateral play ofthe back rest carrier consist of two wedges whose bevelled surfaces lieapart, whose parallel outside surfaces adjoin the housing wall on oneside and on a side of the back rest carrier on the other side, andwhereby the wedge adjoining the housing wall is spring-loaded on itswider end. The spring-loaded wedge presses its bevel against the bevelof the wedge that adjoins the back rest carrier, so that a force isapplied laterally to the back rest carrier and brings it to adjoin thehousing or a part connected to same. Thus, the back rest carrier canslide without play.

According to a preferred embodiment of the invention, inside thehousing, a base plate is fastened in which the other side of the backrest carrier is guided and which supports the spring for the wedgeadjoining the housing wall. The base plate contains guidance means, suchas grooves, for guidance components such as journals, of the wedgeadjoining the back rest carrier.

To prevent that the back rest is unintentionally pulled out of thehousing, another indentation or opening is arranged, in addition to therow of indentations or openings, laterally at the bottom end of same,and above this indentation or opening a spring-loaded locking means isarranged for engaging in the further indentation or opening. Preferably,the locking means is a detent arm which locks when the back rest carrieris pulled upward and releases the back rest carrier again when it ispushed in. For example, this detent arm can be pivotably mounted in thebase plate.

The invention is described below by way of example and with reference tothe drawings, in which:

FIGS. 1 to 3 show three views of a height adjustment including a topview in FIG. 1 with the upper housing part cut away, in FIG. 2 a sectionalong the line A--A, and in FIG. 3 a section along the line B--B of FIG.1;

FIGS. 4a to 6c show separate components from FIG. 1.

The height adjustment according to FIGS. 1 to 6c consists of a flathousing 1, with a substantially rectangular cross section, in which aflat back rest carrier 2 is slidably guided and can be clamped. Thehousing can be extended at the bottom and connected to a seat carrier.It can also have different dimensions than those shown, and it can havea curved shape.

Along its center axis, back rest carrier 2 is provided with a number ofholes 3 which define the insertion depth. In one of these holes 3 is adetent ball 4 which is pressed into the hole by a clamping bevel 5' of ashuttle 5. The pressure results from a spring 6 which is supported in abase plate 7 fastened in housing 1, for example by means of screws 17 orcatches. Base plate 7 is provided with a groove 16 in which the shuttle5 can slide and on which the side opposite spring 6 comes to a stop. Onthis side, shuttle 5 is adjoined by a push-button 8 with which it can bepushed back against the force of spring 6, upon which clamping bevel 5'releases the ball 4, and the back rest can be moved until the desiredinsertion depth is reached, and the push-button 8 is released again.Push-button 8 has a flat recess 8' in which a small spring 9 engagesduring installation, which means that push-button 8 can no longer bepulled out. This measure prevents the unintentional release ofpush-button 8 and provides an opportunity to insert different shapes ofpush-buttons in the same height adjustment without problem. Since thebase plate 7 is preferably made of plastic, a metal washer 21 isinserted in the area where the detent ball 4 pushes against the clampingbevel 5', to ensure proper functioning at all times.

Base plate 7 extends from the side of the push-button 8 across a largeportion of the base surface of housing 1; it has a running surface and astop edge for back rest carrier 2. On the other side, back rest carrier2 adjoins at a step 11' the straight side of a wedge 11 whose bevel 11"adjoins bevel 10" of a second wedge 10, which in turn adjoins the insidehousing wall with its straight side. The second wedge 10 isspring-loaded at its wide end with a pressure spring 12 which issupported in a ledge 13 of the base plate. The spring 12 pushes wedge 10upward as shown in FIG. 1, which via bevels 10" and 11" conducts alateral force onto back rest carrier 2, which is thus guided withoutplay. Base plate 7 is provided with grooves 15 which are open toward thefirst wedge 11 and slidably accommodate guide journal 14 (FIG. 4c and4e). Thus, this wedge 11 is guided and cannot give way.

The height adjustment is provided with a pull-out lock which is shown inFIGS. 1 and 3 in staggered position. This pull-out lock has a hole 22which actually must lie next to the last hole 3 for the detent ball orin FIG. 1 even below it. Arranged above this hole 22 in a recess 18 ofbase plate 7 is a pivotable detent arm 19 which is spring-loaded with aspring 20 supported in base plate 7 in such a way that its catch 19'--asshown in FIG. 3--is pressed into hole 22 as soon as the back rest ispulled out far enough. Then the back rest is blocked. Detent arm 19 doesnot prevent it from being pushed in, since it has a bevel in thatdirection.

I claim:
 1. A back rest on a chair having a height adjustment mechanismthereon, comprising a housing in which a flat back rest carrier is heldby a detent ball clamping arrangement, the back rest carrier beingprovided with successively arranged indentations or openings for adetent ball held in the indentations or openings by means of a clampingbevel engagable with the detent ball and a spring normally urging theclamping bevel into engagement with said detent ball, and the clampingbevel being disengaged from the spring loading by a push-buttonlaterally extending from the housing, the housing carrying spring-loadedback rest carrier lateral play prevention means engaged with the backrest carrier for preventing lateral play movement of the back restcarrier in the housing.
 2. A back rest in accordance with claim 1, inwhich the lateral play prevention means comprises two wedges each havingan inner bevel face, the inner bevel faces of the wedges being engagablewith each other, outside faces of the two wedges being parallel witheach other, the outside face of one wedge adjoining a wall of thehousing, the outside face of a other of the wedges adjoining a side ofthe back rest carrier, and the said one wedge being spring loaded at awider end thereof with a spring carried in said housing and engaged withsaid one wedge wider end, said spring acting to push said one wedge tomove its bevel face against the bevel face of said other wedge whereby alateral force can be conducted from said other wedge to the back restcarrier.
 3. A back rest in accordance with claim 2, in which the housingincludes a base plate in which an opposite side of the back rest carrieris guided; the spring being supported in said base plate.
 4. A back restin accordance with claim 3, in which the base plate is provided withguidance means for guidingly receiving guidance components carried onthe said other wedge, therewith to guide a movement of said other wedge.5. A back rest in accordance with claim 3, in which the detent arm ispivotably mounted in the base plate.
 6. A back rest in accordance withclaim 1, in which in addition to the row of indentations or openings, inthe back rest carrier, a further indentation or opening is carriedtherein, a spring-loaded locking means being carried in the base platefor engaging in said further indentation or opening to maintain the backrest at a selected height adjustment.
 7. A back rest in accordance withclaim 6, in which the locking means is a detent arm which engages insaid further indentation or opening when the back rest carrier is pulledin one direction and releases therefrom when the back rest carrier ispushed in an opposite direction.
 8. A back rest in accordance with claim7, in which the detent arm is pivotably mounted in the base plate.